Patent GB-1395424-A (GB)
Title: Pipette
IPC: A61M5/34
Filed: 1972-06-14
Abstract: 1395424 Vacuum pumps O A SUOVANIEMI 14 June 1972 [23 June 1971] 27735/72 Heading F1N [Also in Division B1] A pipette, which comprises a body, a graduated pipette tube at one end, a manually operable knob at the other end and a plunger which is movable longitudinally of the pipette in one direction by pressure upon the knob against the action of a spring thereby to reduce the volume of an air chamber within the pipette whereby liquid contained in the pipette tube is discharged therefrom and, upon releasing the knob, in the opposite direction by the action of the spring thereby to increase the volume of the air chamber whereby liquid may be sucked into the pipette tube, is characterized in that the longitudinal wall of the body comprises an outer cylindrical member having a screw thread on the inner surface thereof an an inner cylindrical member having a screw thread on the outer surface thereof co-operating with the screw thread on the outer cylindrical member whereby, on rotating the cylindrical members relative to one another about their common axis, the extent of the maximum longitudinal movement of the plunger is varied thereby to vary the volume of liquid which may be sucked into and discharged from the pipette tube. In each of the embodiments of pipette illustrated in Figs. 1 and 2, the body of the pipette comprises an inner cylindrical member 1 provided with a longitudinal scale, an outer cylindrical member 2 provided with a circular scale 14, a locking sleeve 15 and a transparent ring 13 through which may be seen the longitudinal scale which, together with the circular scale, constitutes a micrometer screw scale by means of which the volume of liquid sucked into and discharged from the pipette may be determined. Attached to the inner cylindrical member is an extension 4 to which is removably attached a calibrated pipette tube 7. Located within the pipette is a cylinder 3 which in part defies an air chamber containing a piston 5 and sealing 0-ring 6, the piston being attached to a rod 9 which, together with the piston, constitutes a plunger; the rod, which terminates in a knob 8, is surrounded by a helical spring 11 and is provided with an adjustable stop member 17 by means of which the position of the piston in the cylinder when the piston is urged in the direction of the knob by the spring may be suitably chosen when assembling the pipette. As illustrated in Fig. 1, an end-wall 19 of the air chamber may be provided with a non-return valve 18 and an orifice 20 having a restricted crosssection in order to allow rapid movement of the piston against the action of the spring upon operation of the knob but, upon release of the knob, to prevent rapid return movement of the piston under the action of the spring. The pipette may further comprise a sleeve 10 having a flange which is urged by a helical spring 12 against a wall member 16 having an axial bore in which the sleeve is located. A further embodiment of pipette illustrated in Fig. 3 (not shown) is similar to the embodiment illustrated in Fig. 2 except that it contains neither cylinder nor piston, the air  chamber being constituted by the bore in the extension and the plunger being constituted solely by an end portion of the rod which is received directly in the bore.